Tiptap: mergeAttributes() turns an own __proto__ key into inherited executable DOM attributes

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary @tiptap/core's public mergeAttributes() helper uses ordinary bracket assignment on keys returned by Object.entries(). An own proto key from JSON therefore invokes the legacy prototype setter on the fresh merged object. The function returns an object whose prototype is attacker-controlled, while Object.keys() and ordinary own-property checks show no attacker attributes. When that result is used as a ProseMirror DOMOutputSpec attribute object, prosemirror-model's DOMSerializer.renderSpec() enumerates it with for...in and applies inherited values with setAttribute(). In a browser proof, inherited src and onerror values were copied to an <img and the error handler executed once. This is per-object prototype manipulation; the proof does not modify global Object.prototype. Root cause The affected loop is conceptually: Object.entries(JSON.parse('{"proto": {...}}')) includes proto. Reading mergedAttributes['proto'] resolves the inherited Object.prototype; assigning to the same key…

Published by the source

2 Sep 2026, 14:44 UTC

Last modified by the source

2 Sep 2026, 14:44 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-cp6q-959q-f8rh

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# Patch Next advisory brief: GHSA-cp6q-959q-f8rh

Advisory: Tiptap: mergeAttributes() turns an own __proto__ key into inherited executable DOM attributes
IDs: GHSA-cp6q-959q-f8rh
Record: https://patchnext.com/advisories/ghsa-cp6q-959q-f8rh (revision 1, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @tiptap/core 3.30.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @tiptap/core: affected >= 2.0.0-alpha.0, < 3.30.4; fixed in 3.30.4

## Suggested inspection (read-only)
- `npm ls @tiptap/core --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @tiptap/core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-cp6q-959q-f8rh (GitHub-reviewed advisory GHSA-cp6q-959q-f8rh lists affected ranges: npm @tiptap/core >=2.0.0-alpha.0 <3.30.4)

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